1. Field of the Invention
The present invention relates to a process for automatic alignment of two objects which are to be adjusted with respect to one another, particularly for the automation of mask adjustment in oreder to be able to precisely position the structure of the mask with respect to the structure on a disk in a disk illumination in semiconductor fabrication.
2. Description of the Prior Art
In semiconductor technology, and in many other applications, for example in the manufacture of structured plates for scales, one is confronted with the task of aligning two structured plates with respect to one another with high precision. For example, it is a matter of two substrate plates of which at least one is transparent and of which both bear a pattern on one surface. In semiconductor technology, in general, in which a semiconductor disk already carries a first pattern on its surface and is coated on that surface with a light-sensitive lacquer, a second pattern contained in a mask must be translated into a position which is precisely adjusted with respect to the first pattern.
The translation can be carried out by means of contact illumination, gap illumination or projection illumination. In gap illumination, which at present has the greatest significance attached thereto, a gap of about 20 .mu.m exists between the mask and the disk in order to avoid mask damage. This renders the visual adjustment of mask structures with respect to disk structures more difficult since only one structure can be sharply imaged or, respectively, the sharpness plane lies between the two structures.
Normally, special adjustment marks are employed for the mutual alignment of the mask to the disk through the utilization of two adjustment microscopes which are arranged at a fixed distance.
In the German Pat. No. 1,919,991, an arrangement is illustrated and described in which the automatic alignment of two plates having structures is possible with only three or even only two measuring systems.